There will be no red carpet for Adam Curtis when his film The Power of Nightmares receives its gala screening at the Cannes Film Festival on Saturday. There would be no point: his film has no leading ladies who could disport themselves in backless numbers or lantern-jawed himbos to vogue fatuously before the snappers. Unless, of course, two of his chief protagonists, Osama bin Laden and Paul Wolfowitz, could be prevailed upon to pose together for the world's press on the Grand Palais steps.

"They did offer the full carpet treatment, but I declined," says Curtis. "I just had this horrible thought of me plodding up the steps and lenses dropping all around me." And yet the screening at Cannes is a great honour for Curtis. "They're suddenly talking about me as an auteur," he says. "I just think I'm a journalist. I do feel a bit like an animal in a zoo that's been put in the wrong cage and they'll find out and all go, 'Oi! that's not a giraffe, it's a vicuna!'" A vicuna, as you will know, is a llama-like ruminant.

Last year, Fahrenheit 9/11, Michael Moore's documentary, described by the Guardian's Peter Bradshaw as a "barnstorming anti-war/anti-Bush polemic tossed like an incendiary device into the crowded Cannes festival", won the Palme d'Or. This year something more discreet, but perhaps no less incendiary, is go ing to go off at Cannes in the form of Curtis's Bafta-winning documentary. Like Star Wars: Episode III - Revenge of the Sith and Woody Allen's Match Point, Curtis's film is not in competition, but it is nonetheless this year's Fahrenheit 9/11, shaking festival-goers out of their aesthetic reveries with a political analysis of the causes and consequences of the attacks on the World Trade Centre and the Pentagon.

Curtis does not care for the Moore parallel. "Moore is a political agitprop film-maker. I am not - you'd be hard pushed to tell my politics from watching it. It was an attempt at historical explanation for September 11. You see, up to this point nobody had done a proper history of the ideas and groups that have created our modern world. It's weird that nobody had done before me."

He was asked to trim half an hour off his three-hour series so that it could be shown at Cannes as a film by the festival's artistic director Thierry Frémaux, who in turn had been lobbied by Tom Luddy, who runs the Telluride Film Festival, and Bertrand Tavernier, the great French director and documentary maker. "I know they both liked the BBC series I did before, called The Century of the Self [about the growth of the mass-consumer society in Britain and the US]." Was it hard to edit the series for Cannes? "If you spend six months making three films that you think have a coherent argument, you become convinced that there is nothing that can come out because it's all so wonderful," he says. "But I think the new version works - it has been updated and it makes the argument more powerful." Are you looking forward to being feted on the Côte d'Azur? "I don't know what to expect. I've never been to Cannes before. It's not really a place for the likes of me."

His documentary took as its starting point the year 1949, when two men who would prove massively influential to the establishment of Islamic terror groups and to the neo-Conservative American tendency that now dominates Washington were both in the US. One was an Egyptian school inspector called Sayyid Qutb whose ideas would directly inspire those who flew the planes on the attacks of September 11. Qutb's summer visit to Colorado revolted him so much - he could see nothing there but decadent materialism - that he went home thinking that modern liberal freedoms were eroding society's bonds and that only a radical Islam could prevent its destruction. Meanwhile, in Chicago, an obscure political philosopher called Leo Strauss was developing a similar critique of western liberalism (though without the Islamic answer to individualism's purported ills). He called on conservative politicians to invent national myths to hold society together and stop America in particular from collapsing into degraded individualism. It was from such Straussian reflections that the idea that the US's national destiny was to tilt against seeming foreign evils - be they the Soviet bloc or, later, fundamentalist Islam - was born.

But the film is even more incendiary for its analysis of what Curtis controversially insists is the largely illusory fear of terrorism in the west since 9/11. Curtis argues that politicians such as Bush and Blair have stumbled on a new force that can restore their power and authority - the fear of a hidden and organised web of evil from which they can protect their people. In a still-traumatised US, those with the darkest nightmares have become the most powerful and Curtis's film castigates the media, security forces and the Bush administration for extending their power in this way. "It has really touched a nerve with people who realise something is not quite right with the way terrorism has been reported."

For these reasons, one might well think that The Power of Nightmares would provide a usefully chastening corrective to the prevailing orthodoxy if it were shown on US television. But it seems extremely unlikely that it will be. While a two-and-a-half -hour film version is to be given a prime-time Cannes screening, and while the original three-hour series will be shown tonight on al-Jazeera along with a live interview with the director, US telly has run scared from showing it. "Something extraordinary has happened to American TV since September 11," says Curtis. "A head of the leading networks who had better remain nameless said to me that there was no way they could show it. He said, 'Who are you to say this?' and then he added, 'We would get slaughtered if we put this out.'" Surely a relatively enlightened broadcaster like HBO would show it? "When I was in New York I took a DVD to the head of documentaries at HBO. I still haven't heard from him." He has little hope that he will.

Did the BBC have similar com punction about commissioning the series? "No. And the response from viewers was overwhelmingly positive. Ninety-four per cent of the emails were in favour." That said, some comments on the BBC message boards for Curtis are less enthusiastic. Iain Foster from Portsmouth wrote: "I have sat through your documentary tonight. I hope your programme is shown again following the next terrorist attack. You sound like the hedgehog who claims that cars won't hurt you!!!! I'm amazed!!!!!!!" But the repeat screenings for the series on the BBC show a very different attitude towards The Power of Nightmares from what is prevalent on US TV. "What happens on US TV now is that you have a theatre of confrontation so that people avoid having to seriously analyse what the modern world is like - perhaps because of the emotional shock of September 11," says Curtis. "People take so-called left or right positions and shout at each other. It's almost like the court of Louis XIV - people taking elaborate positions and not thinking very much."

And yet the documentary's success in being selected for Cannes has resulted in Pathé buying up distribution rights to exhibit The Power of Nightmares in cinemas around the world. "They think there's a massive market for this." As a result, there is every possibility that his film will be shown in American cinemas, though Curtis worries that it will as a result become marginalised to art houses. As with the Channel 4 drama Yasmin about a Muslim Yorkshirewoman's travails in post 9/11 Britain, it seems important that the topical Power of Nightmares be seen by as many people as possible rather than savoured by a relatively small number of aesthetes in indie houses. "I work in TV because it's a more powerful medium and it reaches more people. It would be good for it to be shown on American TV, though they might think it's a bit dull to stimulate discussion. Are they too frightened to have the debate?"

Curtis argues that there is a huge appetite for a serious critical analysis of the post-9/11 geopolitical world in the US. "It has been shown at the Tribeca and San Francisco film festivals. All the shows were sold out. There were queues around the block, and the discussions were extraordinary. Sometimes I would just sit back and let the audiences discuss it. But I was quite shocked that the audiences, very well-educated people mostly, did not know about Qutb, whose thinking, which was developed under torture in Egyptian jails, was a direct influence on Zawahiri, al-Qaida's number two. "

How will al-Jazeera's audience respond to the uncut version tonight? "No idea." Perhaps Osama will be tuning from his mystery hideout in Pakistan? "I'm sure he'd find it enlightening."

· The Power of Nightmares will be shown in three-hour form on al-Jazeera tonight, and at Cannes on Saturday.